This application relates to lamp drive circuits and has particular application to portable, battery-powered lamps, such as spotlights. In particular, the application deals with overheating protection for such lamps.
Many lamps, particularly high intensity lamps, including spotlights, can generate considerable heat in use. This heat may reach levels which create serious burn hazards to users, as well as risking damage to lamp components. Some lamps have user-selectable intensity or brightness controls which permit the lamp brightness level to be selectively reduced This could be useful when the lamp becomes excessively hot to the touch, but it is not of much use in protecting against overheating of lamp components, since the user typically has no way of knowing whether the temperature of the components has reached a dangerous level.
It is known to provide protection circuitry for lamps which is responsive to excessive temperature or current conditions to either turn off the lamp or reduce its brightness or intensity level to permit the lamp to cool. These devices commonly use thermistor-type dimming circuits or, in the case of high-intensity discharge lamps, may vary the lamp frequency. Also, such prior lamp drive circuits are typically designed for lamps powered by a fixed source voltage and operation of the lamp at other source voltages.